1. Field of the Invention
The present invention relates to a driver dozing preventing apparatus for preventing drivers from dozing, and particularly to an alarm output device for outputting an alarm when a driver's doze is detected.
2. Description of the Prior Art
A conventional driver dozing preventing apparatus detects a signal indicative of a vehicle behavior such as a steering angle or the like, and signals indicative of driver's physiological changes such as blinking, brain waves, skin potential activity, etc., to thereby determine a reduction in the degree of driver's awakening or wakefulness and produce or issue an alarm when it determines that the degree of driver's wakefulness has been reduced.
An apparatus for determining based on blinking whether the degree of driver's wakefulness is reduced and outputting an alarm when it is determined that the degree of driver's wakefulness has been reduced, has been described in JP-A Nos. 6-219181 and 6-270711, for example.
FIG. 14 is a block diagram showing the structure of the conventional driver dozing preventing apparatus disclosed in JP-A No. 6-270711. In the drawing, reference numeral 10 indicates an opened/closed eyes detecting means for detecting whether the driver's eyes are in an opened or closed state. Reference numeral 20 indicates a closed-eyes duration measuring means for measuring the duration of the state of the closed eyes when the driver is in the closed-eyes state. Reference numeral 30 indicates a characteristic amount calculating means for calculating a feature or characteristic amount for characterizing the degree of driver's wakefulness. Reference numeral 40 indicates a determining means for determining, based on the characteristic amount calculated from the characteristic amount calculating means 30, whether the driver is being awakened. Reference numeral 50 indicates a warning means for producing an alarm when the determining means 40 determines or judges the driver as being in the wakefulness-reduced state.
The operation of the driver dozing preventing apparatus shown in FIG. 14 will next be described. The opened/closed eyes detecting means 10 detects whether the driver's eyes are open or close. When the opened/closed eyes detecting means 10 detects that the driver's eyes are closed, the closed-eyes duration measuring means 20 measures a closed-eyes lasting time during which the closed-eyes state continues.
Further, the characteristic amount calculating means 30 calculates an accumulated or integrated value of the closed-eyes duration corresponding to the amount of characteristic for characterizing the degree of driver's wakefulness, based on the value measured by the closed-eyes duration measuring means 20. Based on the calculated characteristic amount, the determining means 40 makes a decision as to whether the driver is being awakened. When the integrated value per predetermined time (one minute in the present apparatus) is greater than a predetermined quantity (10 seconds in the present apparatus) in this case, the determining means 40 judges the driver as being in the wakefulness-reduced state. When the determining means 40 determines that the driver is in the wakefulness-reduced state, the warning means 50 outputs an alarm.
The conventional driver dozing preventing apparatus is accompanied by a problem that since an alarm sound outputted when the degree of driver's wakefulness is judged as low, is monotonous, the driver becomes accustomed to the output alarm sound if the alarm sound is repeatedly outputted over a long time, so that the apparatus cannot achieve the function of preventing dozed driving.